Strip tape

ABSTRACT

The present invention is drawn to a strip tape which does not undergo lowering of bonding force and which does not cause pollution of the natural environment, working environment, etc. The strip tape includes a center layer containing a polar resin, and at least one polyolefin layer laminated, via a bonding layer, on each face of the center layer. The bonding layer contains an ethylene-methacrylic acid-alkyl acrylate random copolymer. Since the strip tape includes a center layer and at least one polyolefin layer, the interlayer bonding force of the strip tape is high, the bonding strength between the center layer and the polyolefin layer can be increased, and the waterproofing property of the strip tape can be enhanced. Even when a packaging container including the strip tape is heated or cooled sharply during use, the interlayer bonding force of the strip tape is not lowered.

TECHNICAL FIELD

[0001] The present invention relates to a strip tape for a liquid foodcontainer, and more particularly to a strip tape for strongly bonding,within a packaging container for storing liquid food, overlap portionsof a packaging material.

BACKGROUND ART

[0002] Conventionally, most packaging containers for storing liquid foodsuch as milk, juice, liquor, cola drink, or coffee are formed by foldinga packaging material prepared from a laminate including paper, plastic,metallic foil, metal-deposited film, etc., in combination. Edge portionsof the folded packaging material are overlapped with each other andwelded. In order to prevent liquid food from leaking or oozing throughthe overlap portions to the outside of the packaging container, theoverlap portions facing the interior of the packaging container arestrongly bonded together by use of a strip tape.

[0003] The strip tape is formed of, for example, a laminate including acenter layer of a polar resin and a polyolefin layer laminated on eachface of the center layer. When the laminate is formed, at least one ofthe center layer and the polyolefin layer is subjected to anchorcoating, and then the polyolefin layer is laminated on each face of thecenter layer. Usually, a thermosetting adhesive obtained by dissolving,for example, a polyester resin in an organic solvent is used as ananchor-coating agent for carrying out the aforementioned anchor coating.

[0004] However, when the strip tape including the center layer and thepolyolefin layer, at least one of the layers being subjected to anchorcoating, is used, liquid food is absorbed in the strip tape from an edgeportion thereof, and thus the interlayer bonding force is lowered. Whenthe packaging container is heated or cooled drastically during usethereof, the interlayer bonding force is further lowered. As a result,the center layer and the polyolefin layer exfoliate from each other,resulting in a deterioration in the function of the strip tape forprotecting liquid food contained in the packaging container. Inaddition, the strip tape having the aforementioned structure has lowthermal stability and poor oxygen-barrier property.

[0005] Moreover, since the aforementioned anchor-coating agent containsan organic solvent, when anchor coating is carried out or when thepolyolefin layer is laminated on each face of the center layer, theorganic solvent disperses, and thus the natural environment or theworking environment is polluted.

[0006] In order to solve the aforementioned problems in relation to theconventional strip tape, an object of the present invention is toprovide a strip tape which does not undergo lowering of bonding forceand which does not cause pollution of the natural environment or theworking environment.

DISCLOSURE OF THE INVENTION

[0007] To achieve the above object, the present invention provides astrip tape comprising a center layer formed of a polar resin, and atleast one polyolefin layer laminated, via a bonding layer, on each faceof the center layer.

[0008] The bonding layer contains an ethylene-methacrylic acid-alkylacrylate random copolymer.

[0009] Since the strip tape includes a center layer and at least onepolyolefin layer laminated, via a bonding layer, on each face of thecenter layer, the interlayer bonding force is high, the center layer andthe polyolefin layer can be bonded together with increased strength, andthe waterproofing property of the strip tape can be enhanced. Inaddition, even when a packaging container including the strip tape isheated or cooled drastically during use thereof, the interlayer bondingforce is not lowered.

[0010] When liquid food is stored in a packaging container produced byuse of the strip tape, the liquid food stored in the packaging containercan be effectively protected, because the center layer and thepolyolefin layer of the strip tape do not exfoliate from each other, andleak or oozing of the liquid food from the overlap portion of thepackaging material can be prevented over a long period of time. Thestrip tape has high thermal stability and improved oxygen-barrierproperty.

[0011] Since the strip tape has high thermal stability and improvedoxygen-barrier property, the thickness of the strip tape can becommensurately reduced, and thus the amount of the raw material forproducing the strip tape can be reduced.

[0012] Also, since the bonding layer does not contain an organicsolvent, the strip tape does not pollute the natural environment or theworking environment, and the risk of fire hazards is reduced.

[0013] Moreover, since anchor coating is not carried out when the striptape is produced, the production process can be simplified, andhigh-speed production can be realized. In addition, the strip tape isnot smudged with an adhesive contained in the anchor-coating agent, andother problems such as blocking do not arise.

[0014] In another strip tape of the present invention, the bonding layercontains an ethylene-methacrylic acid-alkyl acrylate random copolymercontaining methacrylic acid in an amount of 3-5 wt. % and an alkylacrylate in an amount of 0.05-0.2 wt. %.

[0015] In yet another strip tape of the present invention, the bondinglayer contains an ethylene-methacrylic acid-alkyl acrylate randomcopolymer having a melt flow rate of 11-15 g/10 minutes, a density of0.927-0.932 g/cm³, and a Vicat softening point of 68-72° C.

[0016] In still another strip tape of the present invention, the alkylacrylate is either methyl acrylate or ethyl acrylate.

[0017] In yet another strip tape of the present invention, the polarresin is either an ethylene-vinyl alcohol copolymer or a polyester.

BRIEF DESCRIPTION OF THE DRAWING

[0018]FIG. 1 is a table showing the results of measurement of theinterlayer bonding strength of a strip tape.

BEST MODE FOR CARRYING OUT THE INVENTION

[0019] The embodiments of the present invention will next be describedin detail with reference to the drawing.

[0020] The strip tape of the present invention includes a center layercontaining a polar resin. Examples of the polar resin which may beemployed include ethylene-vinyl alcohol copolymers (EVOH), polyesters,vinyl acetate, ethylene-vinyl acetate copolymers, and polyamides.Particularly, ethylene-vinyl alcohol copolymers or polyesters arepreferably used.

[0021] Examples of the polyesters which may be employed includepolyethylene terephthalate (PET), polybutylene terephthalate, copolymersof ethylene terephthalate and ethylene isophthalate,polyethylene-2,6-naphthalate, polyhexamethylene terephthalate, andcopolymers of hexamethylene terephthalate and 1,4-cyclohexanedimethyleneterephthalate.

[0022] The polar resin is used without any treatment. Preferably, thepolar resin is subjected to monoaxial or biaxial stretching, and is usedin the form of film having a typical thickness of about 10-50 μm. Thecenter layer may be the polar resin film, particularly a deposition filmobtained by depositing, for example, silicon oxide (SiO_(x)) or aluminumoxide (Al₂O₃) onto the face of a polyester film. When the depositionfilm is used, the oxygen barrier property of the strip tape can beenhanced.

[0023] In the manufacture of the strip tape of the present invention,both surfaces of the center layer are coated with polyolefin; i.e.,polyolefin layers serving as outer layers are laminated on the centerlayer. Examples of the polyolefin which may be employed includemonopolymers of ethylene or α-olefin (e.g., propylene, 1-butene,1-hexene, 4-methyl-1-pentene, or 1-octene), and copolymers of ethyleneand α-olefin. Particularly, polyethylene (e.g., low-density polyethylene(LDPE), middle-density polyethylene (MDPE), high-density polyethylene(HDPE), linear low-density polyethylene (LLDPE), or linear low-densitypolyethylene produced by use of a metallocene catalyst (mLLDPE)),polypropylene (e.g., homopolypropylene, a propylene-ethylene randomcopolymer, or a propylene-ethylene block copolymer), polybutene-1, orpoly 4-methyl-pentene-1 is preferably used.

[0024] The aforementioned linear low-density polyethylene is producedthrough copolymerization of ethylene and C4-C8 α-olefin serving as acomonomer (preferably α-olefin containing 6 or more carbon atoms, suchas 1-hexene, 4-methyl-1-pentene, 1-heptene, or 1-octene) in the presenceof a metallocene catalyst.

[0025] The aforementioned metallocene catalyst is a combination ofmetallocene and an aluminum compound serving as a promoter, whereinmetallocene is a compound having a structure in which a transition metalsuch as titanium, zirconium, or hafnium is sandwiched by an unsaturatedcyclic compounds containing, for example, a π-electron-containingcyclopentadienyl group or a substituted cyclopentadienyl group, and thealuminum compound promoter is, for example, alkyl aluminoxane, alkylaluminum, aluminum halide, or alkyl aluminum halide. The aforementionedpolyolefin layer is preferably formed from polyethylene, particularlyfrom low-density polyethylene or linear low-density polyethylene of theaforementioned polyolefins.

[0026] The polyolefin is used without any treatment. Preferably, thepolyolefin is subjected to monoaxial or biaxial stretching, and is usedin the form of film having a typical thickness of about 10-200 μm. Inthe strip tape of the present invention, at least one polyolefin layeris formed on each face of the center layer. However, two or morepolyolefin layers may be formed. When two or more polyolefin layers areformed, the polyolefin layers may be formed of identical or differentmaterials. Also, the polyolefin layers may have the same thickness ordifferent thicknesses.

[0027] If necessary, a variety of additives or similar materials may beadded to at least one of the center layer and the polyolefin layer.

[0028] The strip tape of the present invention is formed by laminatingat least one polyolefin layer, via a bonding layer, on each face of thecenter layer. The bonding layer contains an ethylene-methacrylicacid-alkyl acrylate random copolymer containing methacrylic acid in anamount of 3-5 wt. % and an alkyl acrylate in an amount of 0.05-0.2 wt.%, and having a melt flow rate of 11-15 g/10 minutes (JIS K6760), adensity of 0.927-0.932 g/cm³ (JIS K6760), and a Vicat softening point of68-72° C. (JIS K6760).

[0029] Examples of the alkyl acrylate which may be employed includemethyl acrylate, ethyl acrylate, butyl acrylate, hexyl acrylate, and2-ethylhexyl acrylate. Particularly, methyl acrylate or ethyl acrylateis preferably used. An ethylene-methacrylic acid-alkyl acrylate randomcopolymer having the aforementioned properties is produced throughrandom copolymerization of ethylene, methacrylic acid, and an alkylacrylate by means of a customary method for producingethylene-methacrylic acid random copolymers.

[0030] No particular limitation is imposed on the method for laminatingat least one polyolefin layer, via the bonding layer, on each face ofthe center layer, and a customary lamination method is employed.Examples of the lamination method employed include a dry laminationmethod in which at least one of a film containing the aforementionedpolar resin and a film of the aforementioned polyolefin is coated with afilm serving as the bonding layer, and the polar resin film and thepolyolefin film are press-bonded; a sandwich lamination method in whichthe aforementioned polar resin and the aforementioned polyolefin aremelted and extruded from, for example, an extruder, and then laminatedon both surfaces of a film serving as the bonding layer; a sandwichlamination method in which the material of a film for forming thebonding layer is melted and extruded from, for example, an extruder, andthen laminated on both surfaces of a film containing the aforementionedpolar resin, and a film of the aforementioned polyolefin is laminated onthe extruded bonding layer film; and a co-extrusion lamination method inwhich the aforementioned polar resin, the aforementioned polyolefin, andthe material of a film for forming the bonding layer are melted andseparately extruded from dies such as flat dies or circular diesprovided in, for example, an extruder, and are laminated with oneanother.

[0031] The bonding layer typically has a thickness of 5-30 μm. Beforethe polyolefin layer is laminated, via the bonding layer, on the centerlayer, at least one of the center layer and the polyolefin layer may besubjected to corona discharge treatment, in order to further increasebonding strength. The thus-formed strip tape typically has a width of4-30 mm.

[0032] As described above, since the strip tape having theaforementioned structure includes a center layer containing a polarresin and at least one polyolefin layer laminated, by the mediation of abonding layer, on each face of the center layer, the interlayer bondingforce is high, the center layer and the polyolefin layer can be bondedtogether with increased strength, and the waterproofing property of thestrip tape can be enhanced. Even when a packaging container includingthe strip tape is heated or cooled drastically during use of thecontainer, the interlayer bonding force is not lowered.

[0033] When liquid food is stored in a packaging container produced byuse of the strip tape, the liquid food stored in the packaging containercan be effectively protected, since the center layer and the polyolefinlayer of the strip tape are not exfoliated from each other, and, over along period of time, the liquid food never leak or ooze through theoverlap portion of a packaging material. Moreover, the strip tape hashigh thermal stability and improved oxygen-barrier property.

[0034] Since the strip tape has high thermal stability and improvedoxygen-barrier property, the thickness of the strip tape can be reducedaccordingly, and thus the amount of the raw material for producing thestrip tape can be reduced.

[0035] Moreover, since the bonding layer does not contain an organicsolvent, deterioration of the natural environment or the workingenvironment is prevented, and the risk of fire hazards is reduced.

[0036] Furthermore, since anchor coating is not carried out when thestrip tape is produced, the production process can be simplified tothereby attain high-speed production. In addition, the strip tape is notsmudged with an adhesive contained in an anchor-coating agent, and otherproblems such as blocking do not arise.

EXAMPLE 1

[0037] An ethylene-methacrylic acid-methyl acrylate random copolymercontaining methacrylic acid (4 wt. %) and methyl acrylate (0.1 wt. %)and having a melt flow rate of 13 g/10 minutes, a density of 0.930g/cm³, and a Vicat softening point of 70° C. was melted and extrudedfrom an extruder onto each face of a biaxially stretched film(thickness: 12 μm containing an ethylene-vinyl alcohol copolymer, suchthat the thickness of the extruded film was 25 μm, and a low-densitypolyethylene film having a thickness of 12 μm was laminated on theextruded ethylene-methacrylic acid-methyl acrylate random copolymerfilm, to thereby produce a composite film.

EXAMPLE 2

[0038] A film (thickness: 15 μm) of the same ethylene-methacrylicacid-methyl acrylate random copolymer as employed in Example 1 waslaminated on each face of the ethylene-vinyl alcohol copolymer filmemployed in Example 1. Subsequently, a linear low-density polyethylenefilm having a thickness of 20 μm was laminated on the surface of therandom copolymer film, to thereby produce a composite film.

EXAMPLE 3

[0039] In a manner similar to that of Example 1, theethylene-methacrylic acid-methyl acrylate random copolymer employed inExample 1 was melted and extruded onto each face of a biaxiallystretched polyethylene terephthalate film having a thickness of 15 μm,and a low-density polyethylene film having a thickness of 20 μm waslaminated on the extruded ethylene-methacrylic acid-methyl acrylaterandom copolymer film, to thereby produce a composite film.

EXAMPLE 4

[0040] The procedure of Example 2 was repeated, except that apolyethylene terephthalate film (thickness: 10 μm) on which siliconoxide was deposited was used instead of the ethylene-vinyl alcoholcopolymer film, to thereby produce a composite film.

COMPARATIVE EXAMPLE 1

[0041] An anchor-coating agent containing a thermosetting adhesiveobtained by dissolving a polyester resin in an organic solvent wasapplied onto each face of the ethylene-vinyl alcohol copolymer filmemployed in Example 1 such that the thickness of the anchor-coating filmbecame 25 μm after drying, and the applied anchor-coating agent wasdried. Subsequently, the low-density polyethylene film employed inExample 1 was laminated on the anchor-coating film, to thereby produce acomposite film. During production of the composite film, the organicsolvent was released, and thus the working environment was considerablypolluted.

COMPARATIVE EXAMPLE 2

[0042] The procedure of Example 1 was repeated, except that anethylene-methacrylic acid random copolymer containing methacrylic acid(11 wt. %) and having a melt flow rate of 8 g/10 minutes, a density of0.940 g/cm³, and a Vicat softening point of 75° C. was used instead ofthe ethylene-methacrylic acid-methyl acrylate random copolymer employedin Example 1, to thereby produce a composite film.

[0043] The results of evaluation of the strip tape will next bedescribed.

[0044]FIG. 1 is a table showing the results of measurement of theinterlayer bonding strength of the strip tape.

[0045] A test piece (i.e., strip tape) having a width of 15 mm wasformed from each of the composite films produced in Examples 1 through 4and Comparative Examples 1 and 2, a 180-degree exfoliation test wascarried out for each test piece by use of a tensile tester at anexfoliation rate of 300 mm/minute at 23° C. and a relative humidity of50%, to thereby measure the lamination strength between the center layerand the polyolefin layer; i.e., interlayer bonding strength N/15 mm. Theresults are shown in FIG. 1. In FIG. 1, each value shows the average ofthe results of five test pieces formed from each composite film.

[0046] A brick-shaped packaging container for storing milk (innervolume: 200 ml) was formed from a packaging material formed of alaminate (low-density polyethylene film (thickness: 15 μm)/paper (basisweight: 150 g/m²)/ethylene-vinyl alcohol copolymer film (thickness: 12μm)/low-density polyethylene film (thickness: 15 μm)), such that thelow-density polyethylene film laminated on the ethylene-vinyl alcoholcopolymer film provided the inner face of the container. The overlapportions of the packaging material was bonded together by use of a striptape (width: 15 mm) formed from each composite film of Examples 1through 4 and Comparative Examples 1 and 2. The thus-formed packagingcontainer was filled with water (200 ml), and then allowed to stand fortwo weeks. Thereafter, the bonding strength between the center layer andthe polyolefin layer of the strip tape, the polyolefin layer havingcontacted water, was measured in a manner similar to that describedabove. The results are shown in FIG. 1.

[0047] As shown in FIG. 1, the strip tapes produced in Examples 1through 4 have high interlayer bonding strength as compared with thoseproduced in Comparative Examples 1 and 2. In addition, the degree oflowering of the interlayer bonding strength of the strip tapes producedin Examples 1 through 4 is low even after the strip tapes are immersedin water for two weeks.

[0048] The present invention is not limited to the above-describedembodiments. Numerous modifications and variations of the presentinvention are possible in light of the spirit of the present invention,and they are not excluded from the scope of the present invention.

[0049] Industrial Applicability

[0050] The present invention is applicable to a strip tape for a liquidfood container.

1. A strip tape characterized by comprising: (a) a center layercontaining a polar resin; and (b) at least one polyolefin layerlaminated, via a bonding layer on each face of the center layer, wherein(c) the bonding layer contains an ethylene-methacrylic acid-alkylacrylate random copolymer.
 2. A strip tape according to claim 1, whereinthe bonding layer contains an ethylene-methacrylic acid-alkyl acrylaterandom copolymer containing methacrylic acid in an amount of 3-5 wt. %and an alkyl acrylate in an amount of 0.05-0.2 wt. %.
 3. A strip tapeaccording to claim 2, wherein the bonding layer contains anethylene-methacrylic acid-alkyl acrylate random copolymer having a meltflow rate of 11-15 g/10 minutes, a density of 0.927-0.932 g/cm³, and aVicat softening point of 68-72° C.
 4. A strip tape according to claim 2,wherein the alkyl acrylate is either methyl acrylate or ethyl acrylate.5. A strip tape according to any one of claims 2 through 4, wherein thepolar resin is either an ethylene-vinyl alcohol copolymer or apolyester.